1. Technical Field
The present invention relates to a magnetic recording device comprising a plurality of magnetic disks (hereinafter referred to as disks), a spindle motor for rotatably driving the disks, an assembly of magnetic heads (hereinafter referred to as heads) for writing and reading data on the disk surfaces, an actuator of the head, and control means for positioning the heads on the disk surfaces accurately.
2. Background Art
The prior magnetic recording devices utilized a large storage capacity and operated at a high access time. A plurality of disks having a diameter of approximately 5.25 to 10 inches are mounted in the prior art device. Further, the spindle motors for rotating the disks at a desired speed may be an in-hub motor which is stored in a hub coupled to the disks, or as in a large-sized device, the power may be transmitted by an external motor through belts. A voice coil motor may be utilized as a head actuator for effecting high speed access. The positioning of the head is effected by utilizing the servo surface and the like.
It is impossible to manufacture the above prior art device in a small size. More particularly, in the hub motor device it is necessary to provide a low stiffness spindle motor which is cost inefficient. In a belt driven motor the spindle motor requires frequent maintenance checks to insure transmission of the power through the belt, therefore, such magnetic recording devices become large-sized and thick in order to effect a large capacity and a high speed access. Furthermore, if such a magnetic recording device is thin, the mounting area of the circuit substrate is reduced by the areas of the spindle motor and the head actuator, thereby making it impossible to mount the data separator and the disk controller on the circuit substrate while at the same time providing a small thin magnetic disk device in which the interface for the host computer is provided for a large capacity and high speed access.
FIG. 1 is a sectional view of the main part of the spindle motor utilized in the prior art magnetic recording device. A hub 2 is secured at one end of a shaft 1. A plurality of disks 3 are mounted on the hub 2 by a disk clamp plate 5 separated by disk spacers 4. A rotor yoke 6 is secured at the other end of the shaft 1. A rotor magnet 7 is secured to rotor yoke 6. A stator core 8 is disposed at a distance from the inner side of the rotor magnet 7. Stator coils 9 are wound around the stator core 8. Shaft 1 is supported at a bearing 10 and is sealed against dust by a seal 11.
Bearing 10, the seal 11 and the stator core are provided in a housing 12. The rotor magnet 7 is magnetically divided and magnetized in a plurality of polarities in the radial direction. The positioning of the rotor magnet 7 is detected by a magnetic sensor (not shown). The current is sequentially supplied to the stator coils 9 which are wound around the stator core 8 having a plurality of slots dividing the core into a plurality of phases, thereby generating the rotating power to rotate the shaft 1 and the magnetic disks 3.
The above prior art device has been satisfactory. However, the rotor yoke by necessity is very thick in the magnetic recording device, thus, such a device is not suitable for a small, thin magnetic recording device. Further, since the stator coils are disposed so as to be covered with the rotor yoke, if the number of mounted magnetic disks is increased, the necessary spin-up torque of the spindle motor is increased, and the current supplied to the stator coil is increased. Deviation from the track may thus be caused, and as a result, a portion of the stator coil increases more in temperature, compared with the other portions, and the temperature is not uniform within the magnetic recording device.
Still further, the magnetic recording device has a transducer system comprising disks on which data are recorded and the heads for writing and reading the data in the disk. The heads are secured at the mechanical portion of the system for the movement and the positioning, as hereinafter explained in detail. A plurality of concentric recording areas (hereinafter tracks) are provided on the disks. The data are written and read from the disks by the heads as the heads move relative to the tracks. Therefore, it is necessary to position the head on the tracks accurately in order to write and read the data efficiently and accurately. The more the track density is increased and the narrower the track width becomes, the more accurately the head should be positioned. Therefore, a servo system wherein the head is positioned on the track accurately upon generating the positioning signal of the positioning data recorded on the disk, is widely utilized.
In general, there are several types of servo systems, but in view of the advantages of the excellent positioning accuracy and the short positioning time and so on, the servo system has been widely employed wherein one surface of a disk is utilized for recording only positioning data for controlling the position and the remaining surfaces are utilized for recording the data only. The control surface on which only the positioning data is recorded is hereinafter referred to as a servo surface (a disk surface for the data). These two disks are secured to the spindle motor for rotating. In this system, the magnetic recording device has a head (servo head) positioned relative to the servo surface and a plurality of heads (data heads) positioned relative to the data surfaces. These heads are provided on respective supporting arms, the supporting arm being movable in the radial direction of the disks. The driving motor such as VCM (voice coil motor) is secured at the positioning means. Upon detecting the positioning signal received from the servo head, the VCM is controlled so as to make the difference between the position of the servo head and the position of the destination track as small as possible. The data head is positioned at the destination data track secondarily through the positioning means.
The above method has been satisfactory. It is possible to accurately position the servo head relative to the servo track. However, it is not possible to always accurately position the data head relative to the destination data track.
More particularly, the difference between the relative position of the servo head and the servo track and the difference between the relative position of the data head and the destination data track are caused because the supporting arms between the servo head and the data head, the positioning means and the spindle motor are affected during each operation over time, and because the base frame at which the positioning means, the spindle motor or both are secured is affected due to the variance in the temperature, as well as the difference in the swelling amounts between the piled disks due to the difference in the temperature between the disks. As a result, even if the servo head is positioned accurately at the destination servo track, the data head cannot be positioned at the destination data track accurately.
To solve this problem, Japanese Patent Laid-Open Application No. 51-81603 describes a method of positioning the data head on the destination data track which is widely used. The data head is positioned in accordance with a first positioning signal received from the servo head, superimposing a compensation value, calculated in accordance with a second positioning signal received from the data head, on the first positioning signal, and positioning the data head on the destination track accurately.
However, a further problem may be caused by the above method. More particularly, if the above method is not effected, the head may be positioned by only the first positioning signal received from the servo head. But since the data head may be positioned by the first positioning signal generated from the servo head and adjusting the data head slightly by the second positioning signal, the above method requires more time to adjust the head slightly by the second positioning signal. Furthermore, when the second positioning data is recorded on the data track, for example, on one portion of all of the data tracks, during the time of switching the positioning control by the first positioning data to the positioning control superimposed on the second positioning data, the second positioning data must be recorded by the data head. In fact a waiting time during which the second positioning data on the data surface is rotatingly positioned to the data head is required. For example, when the second positioning data is recorded on only one portion of the data track, the average waiting time is equal to the time for rotating the disk by a half rotation. Further, when a plurality of positioning data are recorded on all the data tracks, the above mentioned waiting time becomes shorter, but such a case does not lead to the essential improvement.
FIG. 20 illustrates the relation between the time for positioning the data head and the change of the location of the data head relative to the destination data track. In FIG. 20, the solid line 828 shows the relationship between the change in position and the time for compensating the head by the second positioning data. The broken line 831 illustrates the track position of the data head in response to the first positioning data. After the data head moves to the track position of a destination data track, the data head requires the four types of operating time for positioning it, that is, the operating time comprising a settling time 832 for converging at the destination position as shown in the broken line 831 with the vibrating transient response (the conversion of the transient response is called settling), the waiting time 833 until receiving the second positioning data the time 834 for moving the head at the data track in accordance with compensated value, and the time 835 for settling the head after positioning the data head on the data track.
If the above improvement is not performed, the data head is completely positioned at the end of the settling time 832. As a result, the above improvement requires a long time for positioning the head in its entirety. Accordingly, it is desirable to provide an improved magnetic recording device which overcomes the shortcomings of the prior art devices described above.